EP0617981A1

EP0617981A1 - Mechanical defibrillation

Info

Publication number: EP0617981A1
Application number: EP94101734A
Authority: EP
Inventors: Kurt Högnelid; Liliane Wecke; Kenth Nilsson; Jan Ljungström
Original assignee: Pacesetter AB; Siemens Elema AB
Current assignee: Pacesetter AB
Priority date: 1993-03-29
Filing date: 1994-02-04
Publication date: 1994-10-05
Anticipated expiration: 2014-02-04
Also published as: US5433731A; DE69413441D1; DE69413441T2; EP0617981B1; JPH06304258A; SE9301055D0

Abstract

An implantable heart defibrillator (1) with a shock pulse generator for delivering a defibrillation shock to a heart (25), the delivered energy being mechanical. The shock pulse generator consists of an electromechanical energy converter (40) which generates e.g pressure, by means of a piezoelement (43), in a pressure chamber (46). Pressure is transmitted by a fluid (57) in an electrode (50) devised like a hydraulic line to a balloon-like electrode head (59) in contact with heart tissue. The generated pressure causes the electrode head (59) to expand and deliver a mechanical shock to the heart (25) corresponding to the pressure.

Description

This invention relates generally to an implantable heart defibrillator. More specifically it relates to a heart defibrillator set forth in the preambula of claim 1.
A modern automatic, implantable defibrillator, e.g. as described in Current Problems in Cardiology, Volume XIV, No. 12, Dec. 1989, Chicago, Troup J.P. "Implantable Cardioverters and Defibrillators", p. 699 ff, especially FIG. 14 and its legend, includes a cardioversion and pacemaker stimulation capability for both tachycardia and bradycardia, in addition to a defibrillation function, and is sometime referred to as an AICD (automatic implantable cardioverter defibrillator). In AICD defibrillation, an attempt is made to induce all heart cells to depolarize simultaneously by imposing a strong electrical field across the heart, i.e. the heart is electrically shocked. The electrical shock takes the form of electrical pulses which can sometimes be emitted in patterns of varying spatial and temporal sophistication.
Achieving depolarization of heart cells by mechanically touching them is also known. The result is a heart beat achieved mechanically. One possible explanation of this phenomenon is that mechanical contact causes leakage from the cellular ion channels. A change then occurs in ion concentrations inside and outside the cell membrane, thereby triggering depolarization and, thus, a heart beat.
However, this knowledge has not found any application in the art of defibrillation which, with the exception of devices for injecting fibrillation-terminating drugs into the heart, e.g. EP-A-429141, has concentrated exclusively on defibrillation by electrical shock.
But considerable electrical energy (about 5 - 40 J) is required for defibrillation. So tissue subjected to the shock could be damaged. For e.g. this reason, the art is attempting to reduce the electrical energy needed for defibrillation.
One procedure for achieving this reduction mechanically is described in US-A-4,925,443, which relates to an artificial, implantable mechanical support function for ventricular compression of the heart. However, any defibrillation necessary in the patient is performed electrically. The mechanical support function is used in conjunction with defibrillation only to compress the heart so a lower level of electrical defibrillation energy can be used.
One object of the invention is to terminate a fibrillation condition in the heart by supplying the heart with a non-electrical shock instead of an electrical shock.
According to the invention, this object is achieved by the features set forth in the characterizing part of claim 1. Here, the mechanical energy in the defibrillation shock induces one or more mechanical shock waves in the heart, thereby subjecting the heart cells to a simultaneous depolarization, which is equivalent to a defibrillation.
Advantageous embodiments of the invention are set forth in the respective dependent claims.
The invention will now be described in greater detail, referring to embodiments in the attached drawings in which

FIG. 1 is a block diagram of a defibrillation system according to the invention;
FIG. 2 shows illustrative examples of patterns for the mechanical defibrillation shock;
FIG. 3 is a schematic of a first embodiment of the electromechanical energy converter with an associated electrode;
FIG. 4 is a schematic of a second embodiment of the electromechanical energy converter with an associated electrode;
FIG. 5 shows a longitudinal cross-section through the electrode according to FIG. 4.

Referring to the block diagram in FIG. 1, an example of a defibrillator according to the invention is shown therein. FIG. 1 shows a defibrillator implant 1 whose enclosure can consist of e.g. a titanium capsule 3. The implant 1 comprises a detection block 5, a pacemaker block 7 capable of delivering stimulation pulses to the heart in both bradycardia and tachycardia, a block for mechanical defibrillation (a shock generator) 9, a block for electrical defibrillation 11, a control unit 13, a diagnostics block 15 and a telemetry block 17, the different blocks/units in the implant 1 communicating internally with one other across a databus 19.
The implant 1 communicates with the outside world, i.e. a programmer 21, via the telemetry block 17, communications primarily comprising programming of the implant 1 and transmission of diagnostic data on e.g. different types of events, sensor signals and ECG signals, from the diagnostic block 15.
The implant 1 is connected to a heart 25 via a system of electrode conductors 23 in order to deliver both pacemaker pulses and shock pulses to the heart, and to receive signals therefrom, indicative of the condition of the heart. Note that FIG. 1 is only a schematic, and signals indicative of the condition of the heart 25 also comprise signals from measurements of physiological variables, such as the partial pressure of oxygen (pO₂) in the blood, from other sites in the body.
As described above, the defibrillation implant 1 includes the functions included in a modern defibrillator (AICD) of the initially described kind, in addition to the mechanical defibrillation block 9, which is described in greater detail below. Thus, the detection block 5 monitors the heart's condition in an IECG monitoring device 27 and in a sensor signal monitoring device 29 in order to detect normal sinus rhythm or abnormal cardiac conditions requiring treatment, e.g. bradycardia, hemodynamically stable/unstable tachycardia and ventricular fibrillation.
Data from the detection block 5 are sent to the control unit 13 which, on the basis of these data, orders the requisite therapy, such as tachycardia-terminating stimulation, and sends a command signal to at least one of the blocks 7, 9, 11, i.e. to the pacemaker block 7 in the exemplified tachycardia-terminating stimulation.
The hitherto described parts and functions of the defibrillation implant 1 are, as noted above, conventional in nature, and will henceforth only be mentioned to the extent that they relate to the mechanical defibrillator/cardioverter 9 (henceforth referred to as the defibrillator) which will now be described.
The block 9 with the mechanical defibrillator consists of a time control unit 31 and a drive unit 33 for the mechanical electrode 50 (FIG. 3). The time control unit 31 makes decision on the pulses, pulse sequences and continuous output signals to be supplied by the defibrillator 9. The drive unit 33 supplies the mechanical electrode 50 with sufficient energy to generate the desired mechanical defibrillation shocks. Examples of such shocks are given in FIG. 2.
FIG. 2a shows examples of different morphologies for individual pulses. As designated with the dashed line for the additional square wave, the pulses can be repeated if necessary.
FIG.2b shows examples of pulse trains or pulse sequences composed of pulses of the kind shown in FIG. 2a, square and triangular pulses in this instance.
FIG. 2c shows examples of different continuous signals which can be supplied in defibrillation of the heart.
The drive unit 33 contains an electromechanical energy converter 40 of the kind shown in FIG. 3. The energy converter 40 has an electromagnetic coil 41, encompassing a moveable rod 42 made of a magnetic material, e.g. soft iron material or permanent magnet material. Any change in current through the coil 41 changes the coil's magnetic field and, thus, the position of the rod 42 in relation to the coil 41.
The electromagnetic converter 40 is functionally closely related to an electrode 50 serving as a line for transmitting mechanical energy from the energy converter 40 to the heart 25.
The outer part of the electrode 50 is devised like a Bowden cable, and its interior consists of a wire 54. The outer part of the electrode 50 consists of a helix 52 made of e.g. MP 35 provided with a protective sleeve 53 made of e.g. silicone rubber or some other biocompatible polymer material. The wire 54, for transmission of the mechanical energy, can move in relation to the interior of the helix 52.
At the distal end of the electrode 50, the sleeve 53 is devised as an elastic, expandable bellows 55 which can also be made of silicone rubber. The bellows 55 prevents blood from penetrating into the electrode 50 during movements of the wire 54. Even if body fluid is thereby prevented from entering the electrode 50, a seal 51 is also provided between the defibrillator implant 1 and the electrode 50, since the electrode, owing to the permeability of the sleeve 53, is filled with a fluid, mainly consisting of deionized water, after implantation.
The wire 54 is attached, at its proximal end, to the rod 42, and, at its distal end, to a mechanical electrode head forming a pressure distribution plate 56 which presses against/is attached to the bellows 55.
The described design according to FIG. 3 achieves mechanical defibrillation of the heart 25 when the time control unit 31, responding to command signals from the control unit 13, orders the drive unit 33 to emit mechanical shocks of the kind shown in FIG. 2 to the heart 25. Changes in current through the coil 41 cause rod 42 movement which is transmitted by the wire 54 and causes a stroke-like movement of the bellows 55, thereby exerting a mechanical action on the heart 25.
The electromechanical conversion of energy can be achieved in some other way than the one described here, e.g. through utilization of the piezo effect or the electro-/magnetostrictive effect. The transmission of power to the wire 54 can also be achieved in some other way than with the described rectilinear movement, e.g. if the wire 54 is affixed to an arm, rotatable around a bearing point, which is acted on by the moving part in the energy converter.
The electrode 50 can be devised with a plurality of distal ends enabling the heart to be defibrillated at a plurality of different sites. The electrode 50 could be e.g. Y-shaped, the wire 54 being subdivided and devised accordingly.
Referring to FIGS. 4, 5, an alternative embodiment is described for the electromechanical energy converter 40 and the electrode 50, which can also be provided with a plurality of distal ends. In this embodiment, pressure is generated in the energy converter 40 when a piezoelectric crystal 43 in same receives electrical energy via two electrode connectors 44 and converts this into mechanical energy in the known way, the mechanical energy, via an elastic membrane 45, generating pressure in a pressure chamber 46. The pressure chamber 46, which is made of a material resistant to pressure deformation, is connected to an electrode 50 devised as a hydraulic line or hose. The electrode 50 has an outer part with a sleeve 53 and a helix 52, as described in conjunction with FIG. 3, although with the difference that the helix 52 is embedded as the core of the sleeve 53, as shown in FIG. 5, so the electrode 50 displays great resistance to pressure. Inside the electrode 50 there is a fluid 57, mainly consisting of deionized water, as previously noted, which serves as a medium for transmitting the pressure generated in the pressure chamber 46. The fluid, which fills the electrode after implantation (any air present diffuses out of the hose after a short time), is connected to one or a plurality of balloon-like sections 59 on the electrode, one such exemplifying section shown at the distal end of the electrode in FIG. 4.
The described design according to FIGS. 4, 5 achieves, as previously described, mechanical defibrillation of the heart 25 when the time control unit 31, according to command signals from the control unit 13, orders the drive unit to emit mechanical shocks of the kind shown in FIG. 2 to the heart 25. The energy converter 40 achieves overpressure in the pressure chamber 46. This supplies pressure which, via the fluid 57, is transmitted to the balloon 59 so it expands in a stroke-like fashion and exerts a mechanical effect on the heart 25.
The energy converter 40 described in FIGS. 4, 5 is, as noted in conjunction with FIG. 3, only one of a plurality of possible converters. Electrode placement can be varied, both in the design in FIG. 3 and the design in FIGS. 4, 5, so electrodes can be applied at e.g. an epicardiac site.
Another way of achieving the desired energy converter 40 in FIGS. 4, 5 is based on electrochemistry and utilizes two electrodes placeable in the fluid 57. When a given electrical charge is passed through the fluid 57, the fluid disassociates, if it consists of deionized water, into hydrogen and oxygen. This gas mixture, when ignited with an electric spark, produces a pressure wave in the fluid. The amount of gas generated in the fluid is strictly governed by the magnitude of the charge supplied, provided the fluid has poor conductivity, which is the case for deionised water. The pressure pulse generated this way is extremely brief, distinct, and well-defined, making it suitable for generation of shock patterns shown in FIG. 2.
Another way of achieving the desired energy conversion entails utilization of the bubble jet art, known from ink jet printers, which can be summarized as follows: The ink in a printer contains a very small heatable plate which can be heated very rapidly (in times measured in µs) with a pulse of current, causing a gas bubble to form on the plate. The increase in volume achieved as a result of the bubble is utilized by the printer for ejecting a drop of ink. Ambient ink causes the gas bubble produced to cool and rapidly collapse. New pulses of current generate new gas bubbles at a rate sometimes exceeding 1 kHz.
When bubble jet technology is utilized in a mechanical defibrillator with a fluid-filled electrode 50 according to FIGS. 4, 5, the heatable plate can be placed either in the electrode 50 or in the drive unit 33. If placed in the electrode 50 in e.g. the balloon 59, the balloon 59 expands when a pulse of current is applied causing gas to develop, and generates a mechanical defibrillation pulse corresponding to the increase in pressure (the balloon then rapidly collapses). As previously noted, these pulses can be chained as shown in FIG. 2.
If the heatable plate is placed in the drive unit 33, a transformation of energy takes place there, and the fluid 57 in the electrode 50 serves solely as a transmission medium for the pulse(s).
Placement of the other energy converters 40, as shown in FIGS. 4, 5 in the electrode 50, is also an alternative.
The mechanical energy converter 40 can also be achieved when the electrode 50 is provided with a piezoelectric element on its distal exterior, which presses against heart tissue and converts the electrical energy into mechanical energy in the known manner. This piezoelectric element can e.g. be in the form of a piezofilm or a ceramic piezoelement. The electrodes 50 can be devised for both intracardiac and epicardiac placement.
As noted initially, the implant 1 contains, in addition to the mechanical defibrillator 9, even other electrical AICD functions. The mechanical defibrillator 9 is devised to collaborate via the control unit 13, with other AICD functions and to provide therapy corresponding to the detected condition of the heart.

REFERENCE DESIGNATION

1.: Defibrillator implant
3.: Titanium enclosure
5.: Detection block
7.: Pacemaker block
9.: Block for mechanical defibrillation
11.: Block for electrical defibrillation
13.: Control unit
15.: Diagnostics block
17.: Telemetry block
19.: Databus
21.: Telemetry block
23.: Electrode conductor system
25.: Heart
27.: IECG monitoring device
29.: Sensor signal monitoring device
31.: Time control unit
33.: Drive unit
40.: Electromechanical energy converter
41.: Electromagnetic coil
42.: Rod
43.: Piezoelectric crystal
44.: Electrode connectors
45.: Elastic membrane
46.: Pressure chamber
50.: Mechanical electrode
51.: Seal
52.: Helix
53.: Protective sleeve
54.: Wire
55.: Bellows
56.: Pressure distribution plate
57.: Transmission medium, fluid
59.: Balloon

Claims

An implantable heart defibrillator (1) with an electrode system (23) comprising a sensing unit (5) for sensing the condition of the heart (25) and for emitting a corresponding condition-sensing signal, a control unit (13) for determining, on the basis of the condition-sensing signal, the condition of the heart (25) and for issuing a command signal if a fibrillation condition is sensed, and a shock generator (9) for supplying energy, in collaboration with the electrode system (23) and depending on the command signal, in the form of at least one defibrillation shock to the heart (25), characterized in that the energy of the emitted defibrillation shock is mechanical.
An implantable heart defibrillator (1) of claim 1, characterized in that the electrode system (23) collaborating with the shock pulse generator (9) has at least one mechanical electrode (50) with an attendant electrode head (56; 59).
An implantable heart defibrillator (1) of claim 1 or 2, characterized in that the shock pulse generator (9) contains a time control unit (31) for configuring the morphology of the mechanical shock (FIG. 2) and the drive unit (33) to the mechanical defibrillation shock.
An implantable heart defibrillator (1) of claim 3, characterized in that the drive unit (33) contains an electromechanical energy converter (40).
An implantable heart stimulator (1) of claim 4, characterized in that the electromechanical energy converter (40) has at least one moving part (42), placeable in the defibrillator (1) enclosure (3), comprising a stroke motion-producing device (41, 42).
An implantable heart defibrillator (1) of claim 5, characterized in that the mechanical electrode (50) comprises an outer part (52, 53) and an inner part (54), the inner part (54) being moveable in relation to the outer part (52, 53), attached at its proximal end to the moveable part (42) in the motion-producing device (41, 42) and attached at its distal end to the electrode head (56), so the stroke movement produced, via the internal part (54) and the electrode head (56) in contact with the heart, is transferred to the heart (25) as a defibrillation shock.
An implantable heart defibrillator (1) of claim 6, characterized in that the external part (52, 53) and the inner part (54) of the electrode (50) consists of a helix (52) and a sleeve (53) or a wire (54) respectively, and the electrode head (56) of the electrode (50) has a pressure distribution plate (56).
An implantable heart defibrillator (1) of any of claims 5-7, characterized in that the stroke-motion producing device (41, 42) achieves its stroke motion with the aid of an electromagnetic, piezoelectric or electro-/magnetostrictive generator.
An implantable heart defibrillator (1) of claim 4, characterized in that the electromechanical energy converter (40) consists of a pressure-generating device (43, 45, 46) placeable in an enclosure (3) for the defibrillator (1).
An implantable heart defibrillator (1) of claim 9, characterized in that the mechanical electrode (50) comprises an outer part (52, 53) and an inner part (57), the inner part is filled with a pressure-transfer medium (57) which is in contact, at its proximal end, with the pressure-generating device (43, 45, 46) and, at its distal end, with the electrode head (59), so the pressure produced via the inner part (57) and the electrode head (59) in contact with the heart is transmitted to the heart (25) as a defibrillation shock.
An implantable heart defibrillator (1) of claim 10, characterized in that the pressure-transmitting medium (57) consists of a fluid (57), and the electrode head (59) consists of at least one elastic, expandable section (59) at the distal end of the electrode (50).
An implantable heart defibrillator (1) of claim 4, characterized in that the electromechanical energy converter (40) consists of a pressure-generating device (43, 45, 46) placeable in the electrode (50) in the area of the electrode head (59).
An implantable heart defibrillator (1) of any of claims 9-12, characterized in that the pressure-generating device (43, 45, 46) generates its pressure with the aid of a piezoelectric, electro-/magnetostrictive, electrochemical or bubble jet generator.
An implantable heart defibrillator (1) of claim 4, characterized in that the electromechanical energy converter (40) is devised for placement on the exterior of the electrode (50) in the electrode head area.
An implantable heart defibrillator (1) of claim 14, characterized in that the electromechanical energy converter (40) placed on the exterior of the electrode (50) is made of a piezoelectric material.
An implantable heart defibrillator (1) of any of the above claims, characterized in that the electrode system (23) is devised to deliver the mechanical energy to the heart (25) at a plurality of points.
An implantable heart defibrillator (1) of any of the above claims, characterized in that the defibrillator (1) additionally comprises at least units for electrical stimulation (7) and electrical shock (11), the mechanical shock pulse generator (9) then being devised to collaborate, via the control unit (13), with units for stimulation and electrical shock.